1. Field of the Invention
The present invention relates generally to ceramic armor used for preventing the penetration of structures by high speed projectiles. The invention relates more specifically to an improved ceramic array armor that provides penetration prevention against multi-hit high speed projectiles.
2. Background Art
Ceramic-faced armor systems are capable of defeating armor piercing projectiles by shattering the hard core of the threat in the ceramic component and terminating the fragment energy in the backing component. After impact, the armor system is damaged. In order for the armor to be capable of defeating subsequent hits with a given proximity to previous hits, the size of the damaged zone must be controlled. In armor systems containing an array of ceramic tiles, cracks cannot propagate from one tile to another if the material between the tiles has an effective impedance much lower than the ceramic. Stress waves can still damage tiles adjacent to an impacted tile by (1) stress wave propagation through the inter-tile material and into the adjacent tiles (2) rapid lateral displacement of ceramic debris from the impacted tile, and (3) the deflection and vibration of the backing material.
Ceramic containing armor systems have demonstrated great promise as reduced weight armors. These armor systems function efficiently by shattering the hard core of a projectile during impact on the ceramic material. The lower velocity bullet and ceramic fragments produce an impact, over a large xe2x80x9cfootprintxe2x80x9d, on a backing plate which supports the ceramic plates. The large footprint enables the backing plate to absorb the incident kinetic energy, through plastic and/or viscoelastic deformation, without being breached.
Most studies of ceramic armors have only investigated single-hit conditions. Interest in ceramic armors, which can protect against multiple hits over small areas of the armor, has been growing.
The challenge to developing multi-hit ceramic armor is to control the damage created in the ceramic plates and the backing plate by the threat impulse. The ability to defeat subsequent hits, which are proximate to previous hits, can be degraded by (1) damage to the ceramic or backing around a prior hit and/or (2) loss of backing support of tile through backing deformation. Early in the impact event, this damage can be created by stress wave propagation from the impact site. Later in the event, the entire armor panel becomes involved with a dynamic excitation from the threat impulse, vibrating locally at first and later the entire panel moving in a fashion similar to a drumhead. This later response of the panel to the threat impulse can cause further damage to the armor system, often remote from the impact site. The later time excitation of the panel is dependent on the support or attachment conditions of the panel. Hence, the development of multi-hit ceramic armors requires consideration of the panel size and the support condition of the panel.
The motivation for this invention comes from the increasing needs for low-cost, mass producible, robust armor system which exhibit exceptional multiple-hit performance, have reliable attachment and show excellent resistance to all hostile environments. The damage produced in ceramic hard face components by projectile impact can be classified into (1) a comminution zone of highly pulverized material in the shape of a conoid under the incident projectile footprint, (2) radial and circumferential cracks, (3) spalling, through the thickness and lateral directions by reflected tensile pulses, and (4) impact from comminuted fragments. Crack propagation is arrested at the boundaries of an impacted tile if the web between the tiles in the tile array is properly designed. However, stress wave propagation can occur through the web and into the adjacent tiles and can still damage the adjacent tiles.
The lateral displacement of ceramic debris during the fracturing of an impacted tile can also damage the adjacent tiles, reducing their capability to defeat a subsequent projectile impact. At late-time, threat impact induces bending waves in the backing material. These bending waves can cause (1) permanent plastic deformation of the backing plate which degrades the support of adjacent tiles, (2) bending fracture of adjacent ceramic tiles, or (3) eject the ceramic tiles from the backing plate.
Stress waves can be attenuated rapidly in viscoelastic materials and in the present invention a continuous elastomeric material surrounding all ceramic tiles is an efficient absorber of the stress waves emanating from the impacted tile. The stress wave propagation in the elastomer filled inter-tile area is determined by the elastomer""s dynamic impedance, which is a function of the strain rate. Unlike metals or ceramics, elastomers (rubbers) can undergo time dependent, recoverable deformations of 5,000% to 10,000% without mechanical failure. They can be stretched 5 to 10 times their original length and, after removal of the stress, retract rapidly to near their original dimensions with no induced damage. This viscoelastic behavior is strongly dependent on the temperature and the strain rate. At low temperatures and/or high strain rates, elastomers display an elastic mechanical behavior, similar to inorganic glasses. At high temperatures and/or low strain rates, elastomers behave like viscous liquids. It is important to select an elastomer exhibiting the rubber behavior, i.e., in the transition zone between glassy and viscous flow states, at high strain rates (102 to 104 sxe2x88x921) and at the temperature corresponding to the ballistic events.
By using elastomer-encapsulation around the ceramic tiles, the ceramic damage zone can usually be limited to the impacted tile. Impacts near to the edge of a tile may produce some damage in the immediately adjacent tile. In the tile array, lateral self-confinement in the impacted tile is created by the surrounding tiles. This self-confinement enhances the resistance to penetration by increasing the xe2x80x9cfrictionxe2x80x9d between the projectile and the fragmented rubbles.
The present invention comprises a new, light-weight armor hard-face component with elastomer encapsulation and lateral confinement to effectively improve the multi-hit performance. The preferred embodiment is an integrated package consisting of a large elastomer plate, which contains confined, shock isolated ceramic tiles. This plate can be formed to a variety of sizes and shapes by cutting the elastomer along the gap between ceramic tiles. The attachment of this integrated package to a vehicle structure can be easily accomplished by bolting or adhesive bonding.
The key approach of this invention is to use elastomer encapsulation to limit lateral damage, to increase ballistic efficiency and to allow multiple impacts without ballistic performance degradation. The armor component is an integrated package, containing a continuous elastomer phase around segmented ceramic tiles. The elastomer is used to (1) attenuate stress waves, (2) accommodate the lateral displacement of ceramic fracturing, and (3) isolate adjacent tiles during the backing vibration stage.
Polysulfide possesses adequate dynamic properties for use as the encapsulation component. At high strain rates, the Polysulfide exhibits the desired rubber behavior, and its excellent mechanical properties maintain the structural integrity of the whole system. In order to provide excellent resistance to all hostile battlefield environments, multiple layers of different elastomers may be used. The surface rubber can provide an excellent resistance against road hazards, fire, gasoline, etc. The interior rubber, which surrounds the ceramic tiles, has the dynamic properties required to protect the tile adjacent to a hit tile.
The module bonding process requires an elastomer bonding process to assemble large panels from small modules. A few standard module sizes, e.g. 4xc3x974 tile module, can be manufactured first. The large panels can be fabricated through bonding these individual standard modules to the backing plate and covering the backing plate like a puzzle. However, the final large panel will not have a continuous spall shield. The spall shield plays an important role in restraining flying fragments in front of the armor. The flying fragment may cause a secondary injury to near-by personnel. A discontinuous spall shield may not be efficient in containing the ceramic fragments. One option is applying a continuous spall shield after the modules are bonded onto the backing. The effects of the discontinuous front-face spall shield and the trade-off of the post process for the continuous spall shield would have to be considered. The module cutting process utilizes a splicing device to slice a big module along the rubber gap, without damaging the ceramic tiles. This approach provides the flexibility for the attachment of custom shapes in the field, and may be convenient for field repairs.
It is anticipated that the large-scaled armor packages implemented in accordance with the invention can be used for stand-alone applique armors, structural armors, ceramic components mounted to a thick vehicle hull as an armor upgrade, vehicle skirts, hard-face armor components in other armor systems and stand-alone+semi-flexible armors.
In another embodiment of the present invention shock propagation is further attenuated by employing a plurality of corner shims.
It is therefore a principal object of the present invention to provide an improved tile array ceramic armor wherein each such tile is encapsulated in an elastomer to increase resistance to multiple projectile hits.
It is another object of the invention to provide an improved ceramic tile array armor wherein an elastomer encapsulation contains and confines each such tile to limit lateral damage, increase ballistic efficiency and enable defeat of multiple impacts.
It is yet another object of the invention to provide an elastomer-encapsulated tile array armor wherein a plurality of divider shims at the tile corners helps to control shock propagation from the impacted tiles to adjacent tiles.